The present invention relates to a laser light scattering photometer for the determination of molecular weight of the solute component in the subjected liquid by detecting the intensity of the scattering light from the liquid. This invention offers equipment for the measurement of the intensity of the scattering light by means of a novel optical system and measuring "cell" structure.
The light scattering method is playing an important role for determining the molecular weight and size of solute-molecule in the solution. This method is not widely used because of the complicated operative techniques for measurement. For instance, it is necessary to extrapolate the concentration and the angle to zero by the Method of the Zim Plot, for example, by measuring the intensity of the scattering light at the angle in the range from 30.degree. to 150.degree. usually as to several samples with different concentrations of the solutions.
In laser light scattering method it is possible to determine the molecular weight without extrapolating technique of both factors as in the above. That is, in the use of laser light scattering photometer, it is possible to measure the intensity of scattering light at a small angle of 5.degree. or lesser angles.
In practice, therefore extrapolation to zero-angle is unnecessary. Futhermore, because of higher intensity of the incident light, very dilute solution can be used as a sample for measurement, thus usually there is no necessity to extrapolate to zero-concentration.
In such a case, the intensity of the scattering light to be measured is proportional to the product of the molecular weight of the solute and the concentration of the solution, therefore, by combined use of laser light scattering photometer as a molecular weight detector with a concentration detector, it is possible to measure the molecular weight of the solute in the subjected solution continuously.
Conventionally known laser light scattering photometers have specific structures especially on the measuring "cell" part, which require special processing acuity, and thus, lacking in practicability. Moreover, the fluctuation of the intensity of the incident light becomes a cause of variation of the intensity of scattering light, thereby, it is difficult to obtain stable measuring values as the dermerit. Then further practical photometers are required.
The present inventors have been making efforts for improving the above defects, and have completed a laser light scattering photometer in featuring the equipment provided with the optical system removing the fluctuation of the itensity of scattered light due to the change of the intensity of the incident light, and its corresponding electronic system as well as the measuring cell with much simpler structure than that of the conventional ones.
In other words, in a laser light scattering photometer for measuring the intensity of scattered light of a subjected testing liquid, a measuring cell and an annular slit equipped with a light trap at the central position are aligned so as to match the axis of the incident beam. A pair of detectors in a receiving optical system monitors the intensity of the light transmitted through the measuring cell and is reflected by the light trap. The second light detector detects the intensity of scattered light at the scattering angle restricted by the annular slit. An electronic circuit eliminates the intensity fluctuation in which the the fluctuation in the intensity of the transmitted light is detected by the detector for transmitted light. The electronic circuit has an output signal corresponding to the fluctuation in intensity of the transmitted light. This output signal is put into the detector for scattered light as input signal. Thus, by the output signal, the fluctuation in the output of the scattered light detector caused by the fluctuation in the intensity of the incident beam is compensated.
The measuring cell is a flow-type cell composed of a cell-composing material having cylindrical beam-passing part perforated to make the central axis matching the axis of a laser incident beam and cylindrically perforated pathway of a testing liquid, connected to the beam-passing part. Two glass blocks are mounted on front and rear faces of the cell-composing material against laser incident beam.